1. Field of the Invention
The invention relates generally to connectors. In particular, embodiments relate to system and methods for tandem motor connections in a submersible pumping system for use in a wellbore.
2. Background Art
Pumping systems driven by motors are used to extract or move fluid and gas. In subsurface operations such as in a wellbore environment, typically submersible electric pumping systems are used in the production of hydrocarbon-based fluids. Unlike conventional motors in surface operations, a motor used in a submersible pumping system needs to be submersed in well fluids. The submersible motor is sealed from surrounding well fluids by a motor protector. The motor and the protector can be a combined section, as in a configuration disclosed in U.S. Patent Application Publication No. 20050109515.
The motor protector may also function to compensate for the motor oil volume change due to temperature and pressure changes during, for example, shipping the motor from a factory facility to an oil field, moving the motor from the surface to the wellbore, and turning on and off the pumping system.
A submersible pumping system in the prior art (U.S. Patent Application Publication No. 20050074331) is illustrated in FIG. 1. The pumping system 10 is located within a wellbore 12 in a geological formation 14 containing fluids such as oil. The wellbore 12 is protected with a casing 16 having perforations 18 through which fluids flow from formation 14 into the wellbore 12. The pumping system 10 includes a centrifugal pump 20 having an intake 22, a submersible motor 24 and a motor protector 26. The system 10 is suspended within the wellbore 12 by a deployment system 28. A power cable 30 provides electric power to the submersible motor 24. When pumping, wellbore fluids are introduced into the intake unit 22, and are passed into an intake on the centrifugal pump 20, and out to a tubing string for discharge to the earth's surface.
In FIG. 1, the pump section is located above the motor section. Other configurations of pumping systems also exist. For example, U.S. Patent Application Publication No. 20050199384 discloses shaft locking couplings for submersible pumping systems with a pump section located below a motor section.
A pumping system can include a plurality of stages connected together. For example, U.S. Patent Application Publication No. 20050074331 discloses an elongated pump with multiple pump stages in order to reduce compression force in each stage. In some operations, two submersible motors are connected together to form a “tandem motor” in order to provide a larger driving force for a pump than a single motor does. U.S. Patent Application Publication No. 20030116323 discloses multiple tandem motors mechanically connected to each other, but electrically independently connected to electrical power sources.
A tandem motor typically includes an “upper tandem motor” and a “lower tandem motor”, wherein the “upper” and “lower” refer to the relative positions of the individual motors with reference to the pump. The two motors and/or protectors can be connected together using a protector-to-protector connection, a motor-to-motor connection, or a motor-to-protector connection. Different sections of a pumping system are typically connected together with bolts, as disclosed in U.S. Pat. No. 5,628,616.
A tandem motor is filled with motor oil for lubrication as in an individual motor. The tandem motor can be filled with oil in a factory before being shipped to an oil field. However, it is a challenge to ship a tandem motor without oil leaking out and air pockets being trapped in the motors due to temperature changes and vibrations. It is often desirable to ship the motors individually, and assemble them into a tandem motor at a well site. The process of filling a tandem motor with motor oil on a rig floor is very time consuming, and human errors during the procedure can leave air pockets trapped in the tandem motor and decrease the motor life span.